1. Technical Field
The present invention relates generally to a video traffic system and, more particularly, to a system for real time transmission of variable bit rate MPEG video traffic with consistent quality.
2. Description of Related Art
It is known that variable bit rate (VBR) video provides more constant quality than constant bit rate (CBR) video (see, e.g., “A Variable Rate Video Decoder For Synchronous Transfer Mode Networks,” by W. Verbiest and L. Pinoo, IEEE J. Select. Areas Commun., Vol. 7, No. 5, pp. 761–770, June. 1989; and “Packet Video, Modeling and Signal Processing”, by N. Ohta, Artech House, 1994). The VBR MPEG (Moving Picture Experts Group) coded video traffic is burst by three different encoding frame types, i.e., I-frame, P-frame, and B-frame as proposed in “Generic Coding of Moving Pictures and Associated Audio: Video”, ISO-IEC/JTC1/SC29/WG11/ NO801rev, MPEG Committee Draft: Rec. H. 262, April, 1995. The VBR video is highly time-variant due to successive scenes having different contents as proposed in “Bandwidth Renegotiation For VBR Video Over ATM Networks,” by D. J. Reininger, D. Raychaudhuri and J. Y. Hui, IEEE J. Select. Areas Commun., Vol. 4, No. 6, pp. 1076–1086, August, 1996.
A video with constant quality can be obtained by transmitting an unconstrained VBR providing similar quantization parameter to all frames, such as proposed in the above reference by D. J. Reininger, et al., as well as “MPEG Coding For Variable Bit Rate Video Transmission”, by P. Pancha and M. El Zarki, IEEE Commun. Mag., Vol. 32, No. 4, pp. 54–66, May. 1994. Since an ATM (Asynchronous Transfer Mode) network provides limited bandwidth, however, the ATM network requires a constrained VBR specified by three parameters of peak rate, sustainable rate, and maximum burst length. Smoothing (or shaping) is one of the most dependable methods that efficiently improves network utilization and achieves constrained VBR transmission at an acceptable delay cost, as proposed in “Performance Models of Statistical Multiplexing In Packet Video Communications”, by B. Maglaris, IEEE Trans. Commun., Vol. 36, No. 7. pp. 834–844, July. 1998, as well as “Analysis of ON-OFF Source Shaping For ATM Multiplexing”, by F. Bernabei, Proc. INFOCOM, pp. 1330–1336, 1993.
In addition to smoothing, bandwidth renegotiation is another important system for the transmission. However, undesirable operation of the smoothing and bandwidth renegotiation may give rise to unexpected encoder buffer overflow, decoder buffer overflow, or violation of the renegotiated bandwidth, which causes unwanted loss of data. The undesirable loss of data seriously deteriorates the transmitted video quality. Therefore, a method for controlling a joint encoder and channel rate is needed which considers an allocated bandwidth and sizes of the encoder and decoder buffers, such as proposed by “Constraints on Variable Bit Rate Video for ATM Networks”, A. R. Reibman and B. G. Haskell, IEEE Trans. Circuit Syst. Video Technol., Vol. 2, No. 4, pp. 361–372, December. 1992; and “Joint Encoder and Channel Rate control of VBR Video over ATM Networks”, W. Ding, IEEE Trans. Circuit Syst. Video Technol., Vol. 7, No. 2, pp. 266–278, April, 1997.
Reininger et al. proposes method for bandwidth renegotiation without traffic smoothing, and an method for controlling encoder rate corresponding to negotiated traffic parameters. Reibman, et al. discloses that constraints imposed on the encoded video bit rate (i.e., encoded video transmission rate) are caused by encoder and decoder buffering. Ding proposes a method for traffic smoothing, joint encoder, and channel rate control, wherein the negotiated peak rate is very large while the employed peak rate is very small. That is, the allocated peak rate is 4 times higher than the rate to have been maintained (about 180 kbits/frame) if the used peak rate is only half of the allocated peak rate. In the methods disclosed by Reibman, et al. and Ding, traffic parameters for bandwidth renegotiation and rate control cannot be obtained by on-line processing. Some techniques for traffic smoothing for VBR MPEG video are disclosed in the following references: “Source Traffic Smoothing and ATM Network Interfaces for VBR MPG Video Encoders”, by K. Joseph and D. Reininger, Proc. ICIP, pp. 1761–1767, 1995); “Adaptive Prediction and Smoothing of MPEG Video in ATM networks”, by S. Jung and J. S. Meditch, Proc, ICC, pp. 832–836, 1995); and “An Algorithm for Lossless Smoothing of MPEG Video” by S. S. Lam, S. Chow and D. K. Y. Yau, ACM SIGCOMM, pp. 281–293, 1994. These techniques, however, have not considered bandwidth renegotiation.